{ INFORMATICS.MCCME.RU
  Problem statement: http://informatics.mccme.ru/moodle/mod/statements/view3.php?chapterid=269
  Verdict: Accepted
}
var a,b,c,d,e,f:longint; x,y,z,p:extended;
begin
assign(input,'input.txt');
assign(output,'output.txt');
reset(input);
rewrite(output);
read(a,b,c,d,e,f);
x:=sqrt(sqr(c-a)+sqr(d-b));
y:=sqrt(sqr(e-a)+sqr(f-b));
z:=sqrt(sqr(e-c)+sqr(f-d));
p:=(x+y+z)/2;
writeln(sqrt(p*(p-x)*(p-y)*(p-z)):0:3);
end.